The protective effect of N-acetyl-cysteine against adriamycin-induced cardiomyopathy has been demonstrated in mice. Further evidence has been obtained to implicate a free radical mechanism for adriamycin-related cardiotoxicity. Glutathione peroxidase, an enzyme crucial to maintenance of free radical defenses in the heart, is rapidly depleted by adriamycin. The mechanism of this depletion is under investigation.